Conventionally, an electronic circuit connected to at least one resonator of a MEMS resonator device can also be used to perform an angular speed measurement. An angular speed may be measured along one, two or three axes, for example, with a MEMS gyroscope. The gyroscope generally includes at least one mass maintained by a structure in the form of a spring and capable of being set in oscillation electrically at a frequency determined by the spring constant with a defined damping factor for the mass. An angular speed can be determined based on the oscillation speed of the mass and the force generated, which is perpendicular to the angular speed and to the oscillation motion of the mass.
To achieve this, there exist electronic circuits enabling the mass to be driven in oscillation at a determined frequency and at a defined amplitude, and for measuring an angular speed in a perpendicular direction to the oscillation of the mass. These electronic drive circuits, which preferably use oscillation in a phase lock loop to drive oscillation along at least one axis of motion of the MEMS resonator as described, in particular, in EP Patent Applications Nos 2 259 019 A1 and 2 336 717 A1. A phase lock loop is used to maintain the oscillation of the resonator mass in a first direction. When a rotational speed is to be measured by a measurement circuit, an oscillation is also generated in a second direction perpendicular to the first direction with a phase shift of π/2 relative to the oscillation in the first direction. No reduction in power consumption can be obtained for maintaining oscillation of the mass and the rotational speed measurement, since a relatively high supply voltage is also required. The start time of such a rotational speed measurement system is therefore slow, which also constitutes a drawback.
Reference may also be made to the electronic circuit for driving and measuring the angular speed of at least one MEMS resonator of a gyroscope on one, two or three axes, which is disclosed in the thesis entitled “System and circuit design for a capacitive MEMS gyroscope” by Mikko Saukoski of Helsinki University of Technology, Faculty of Electronics, Communication and Automation, Department of Micro and Nano Sciences dated 2008 (ISBN9789512292974). As previously, a phase lock loop is used for maintaining the oscillation of the primary resonator mass of the gyroscope, as shown in FIG. 2.9 of page 31. The rotational speed measurement is determined by the secondary resonator of the gyroscope in a direction perpendicular to the motion of the oscillating mass. This does not make it possible to reduce the electrical power consumption of the system, which is a drawback. Several perturbations are also observed between the actuation of oscillation of the mass and the detection of motion of the mass for regulating the amplitude of oscillation without also facilitating the angular speed measurement, which constitutes another drawback.
The document entitled “Force to rebalance control of HRG and suppression of its errors on the basis of FPGA” by Xu Wang, Wenqi Wu, Bing Luo, Zhen Fang, Yun Li and Qingan Jiang, published on 16 Dec. 2011 in Sensors 2011 (ISSN 1424-8220), may also be cited. This document discloses a new concept of adapting force for a hemisphere gyroscopic resonator on the basis of an FPGA. The system disclosed provides for forced oscillation of the mass by a VCO oscillator on the basis of cos(ω·t) and sine(ω·t) signals. The system detects the motion of the secondary resonator, which is defined as the south electrode for powering the primary resonator, which is defined as the west electrode. This therefore cancels out vibration on the primary. In this control loop, phase and amplitude are controlled to supply exactly the power necessary to cancel out the motion of the secondary.
One drawback of this system is that it uses a VCO oscillator. This makes it impossible to reduce the overall electrical power consumption of the system for controlling the phase and amplitude of oscillation and also for the angular speed measurement. Further, the information from the secondary is used to oscillate the primary resonator. This complicates manufacture, and also the precision of the oscillation phase and amplitude control. The primary is dependent on the secondary, which is another drawback.